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Physics 111 Lab #2:

Force and Newton's Laws

Force probes will be used to study the forces exerted by a cart and other objects in the presence of gravitational, spring, frictional, and tension forces (see Lectures 4, 5, 6).

Key Activities:

Measuring Weight with a Force Probe

The relationship between weight and mass will be studied by hanging a series of masses on the force probe (Lectures 4, 5).

Tension and Acceleration of a Coupled Two-Mass System

The tension and acceleration of a "frictionless" cart coupled to a hanging mass will be studied using a motion detector and a force probe mounted on the cart (Lecture 5).

A comparison of the tension between the cart and hanging mass (top) and the acceleration of the cart/hanging mass system (bottom), both when the coupled system is stationary (time < 2 sec) and when the system is allowed to accelerate (time > 2 sec). Notice that the tension between the cart and hanging mass becomes smaller when the cart is released and allowed to accelerate.

What's happening?

Relationship between Force and a Varying Acceleration

A force probe and motion detector, in conjunction with an oscillating hanging mass on a spring, will be used to investigate the relationship between force and acceleration (Lecture 4).

The results for an oscillating 0.35 kg mass illustrate the proportionality between the force on the mass (top), as measured by the force probe, and the acceleration of the mass (middle) measured by the motion detector. The lower plot shows the proportionality constant, m=F/a, which in this example has an average value of 0.37 kg, in rough agreement with the measured mass of the block + spring. When determining the average value, we ignore the "spikes" in the ratio F/a caused when both the force and acceleration approach zero and the value of F/a becomes erratic.

Hooke's Law and the Spring Constant

A motion detector, a cart equipped with a force probe, a spring, and a hanging mass will be used to study Hooke's Law for springs (Lecture 5).

The force exerted by a spring, F, as measured by the force probe, versus the extension of the spring, x, illustrating Hooke's force law, F = - k x, and the determination of the force constant for the spring, k (see Lecture 5).